This map shows the average date that each National Weather Service forecast office issues its first tornado warning every year, based on data from 1986-2013. It's pretty illustrative of how tornado climatology tends to work in the United States. The Deep South sees its first round of severe weather during the winter, and it radiates outwards as the atmosphere begins to warm up through the country.

The earliest average date for the first tornado warning of the year is January 24th, claimed by the NWS in Jackson, Mississippi, and the latest is December 13, claimed by the NWS in Eureka, California.

For reference, the last time the NWS office in Eureka issued a tornado warning was December 15, 2002.

As of Wednesday, NWS Jackson had issued 1,547 tornado warnings since January 1, 2005.